1. Field of the Invention
This invention relates to leak detectors and, more particularly, to leak detectors for pipelines and tanks carrying petroleum products.
2. Description of Related Art
A persistent problem that plagues steel pipelines, (as well as tanks, and other vessels), is corrosion. Thousands of miles of oil pipelines are 75 or more years old. These are steel, and they are constantly corroding. Corrosion is a non-uniform process. Small and large corrosion holes appear at random places on pipes. There are various reasons: One is the non-uniformity of the steel due to localized impurities which cause electrolytic action and erosion of the steel. Another is the nature of oils which may contain water, sulfides, chlorides, and other oxidizing agents which collect locally to corrode piping. Deadhead pipelines, (pipes used intermittently) are particularly susceptible to local corrosion holes. There are many other factors that come into play, and the result is that practically all pipeline sections are observed to reach their end-of-life status with corrosion showing as small or large holes. That fact makes it difficult to statistically analyze the health status of a pipeline or a tank.
A reasonably rapid response system for monitoring and detecting oil spills and leaks would forestall oil spill losses, and it would prevent disasters. A few years ago, one such spill disaster caused enormous ecological damage and nearly a billion dollars of cleanup expenses. Smaller, very costly spills occur frequently, and oil losses also add up. Several patents describe methods of detecting oil spills. Some describe Infrared photography, a commercially available detection/monitoring system employs a cable which is placed under the pipeline to detect and monitor oil spills. Generally, the cost of placing a cable under an existing pipeline is prohibitive because pipelines are mainly underground and the excavation process is very expensive. The present invention is designed to be economically utilized for existing pipelines as well as new pipelines, and to provide means of detecting early stage leaks.
U.S. Pat. No. 4,029,889 by Mizuochi-Shoken describes a coaxial cable encased in a coating of petroleum permeable plastic which is hydrophobic: it will not allow water to penetrate the coating. When oil penetrates the coating, the capacitance between the cable conductors changes, and the change can be measured by an instrument such as a time domain reflectometer instrument. Various versions of this system are now manufactured by companies such as Raychem and Pentair-TraceTek and are presently commercially utilized for oil spill detection. This system has the disadvantage of requiring a system to measure small capacitance changes in a cable, and of locating the oil leak region of the cable. The present invention is designed to provide a simpler detection method and to avoid the complication of measuring capacitance changes. The output of our detector system is the closure of a contact or a voltage pulse either of which is much less expensive to implement in a detection system.